1. Field of the Invention
This invention relates to coated abrasive articles and, more particularly, to such articles which are rendered tear resistant by the use of a multilayer polymer film backing.
2. Description of the Related Art
Coated abrasive articles generally comprise a backing layer to which a multiplicity of abrasive particles are bonded. In one form, the abrasive particles are bonded to the backing by a first binder, commonly referred to as a make coat. A second binder, commonly called a size coat, is then applied over the make coat and the abrasive particles to reinforce the particles. In a second form, the abrasive particles are dispersed in a binder to provide an abrasive composite and the composite is bonded to the backing by the binder.
A wide variety of backings for coated abrasive articles are known including paper, nonwoven webs, cloth, vulcanized fibers, polymeric films and combinations thereof. For example, U.S. Pat. No. 3,607,354, "Method of Delustering Polyethylene Terephthalate Film," issued Sep. 21, 1971 to L. Krogh et al. discloses a biaxially oriented polyethylene terephthalate film for coated abrasives. British patent Specification No. 1,451,331 "Abrasive Sheet Material, " published Sep. 29, 1976 discloses an abrasive sheet backing comprising a laminate of at least one fibrous material (i.e., paper) and a dimensionally stable, preformed plastic sheet (e.g., polyester). U.S. Pat. No. 4,011,358 "Article Having a Coextruded Polyester Support Film," issued Jul. 23, 1974 to G. Roelofs discloses a backing for an abrasive sheet material. The backing comprises a biaxially oriented polyester base layer (e.g., polyethylene terephthalate, polycyclohexanedimethyl terephthalate or polyethylene naphthalate) and a thin layer of a thermoplastic, adhesion-promoting polyester.
U.S. Pat. No. 4,008,278 "Severable Multilayer Thermoplastic Film," issued Mar. 13, 1990 to R. H. Bland et al. discloses films comprising at least 5 alternating layers of brittle and ductile materials. A functional layer such as an abrasive material in a binder may be applied to one or both major surfaces of the film. It is stated that "severable" means that the film may be easily and precisely cut in a straight line with little, if any, stress cracking, whitening etc. along the severed edge.
International Patent Publication No. WO 86/02306 "Coated Abrasive Sheet Material with Improved Backing," published Apr. 24, 1986, discloses an improved backing for a coated abrasive sheet material comprising a flexible sheet (e.g., paper, polyester, polyolefins), a thermoplastic adhesive layer, and a multiplicity of reinforcing yarns.
Polyester films have found wide commercial success as backings, especially in fine grade abrasive articles (i.e., articles having fine size abrasive particles), because the flat, smooth films provide a higher cut rate and a smoother surface finish on the workpiece being abraded. Unfortunately, however, those polyester films which are presently known have limited tear resistance. When the abrasive article is a belt or disk which rotates or vibrates at high speed during use, edges of the backing may become nicked, cut or torn thereby destroying the utility of the article.
Accordingly, there is considerable need for coated abrasive articles having backings with good tear resistance.